Rotor blades for large wind turbines may reach lengths of 80 m or more. The manufacture of such a long rotor blade in one piece is generally not feasible. Furthermore, the transport of a very long rotor blade to a destination such as a wind turbine site can be very problematic and adds considerably to the overall cost of a wind turbine. Therefore, long wind turbine rotor blades may be assembled by connecting rotor blade sections together. A rotor blade section can be manufactured in a more straightforward manner, and the transport of such sections is relatively economical. Since the outer surface of a rotor blade should be as smooth as possible to ensure a favorable aerodynamic performance, any interface elements used to join adjacent rotor blade sections must be arranged in the interiors of the blade sections. These interface elements can be connected together a number of ways. However, the connections between adjacent rotor blade sections are associated with a number of problems.
In one approach, the interface elements are embodied as a slip fitting, i.e. the interface element of one blade section slips into a corresponding interface element of the neighboring blade section, and a high-viscosity adhesive is used to bond the interface sections together. The adhesive must have a high viscosity to ensure that it remains only between the interface elements and that it does not “escape” or spread into interior regions of rotor blade before it hardens. However, air pockets are often trapped in such a high-viscosity adhesive, and these air pockets remain after hardening or curing. The air pockets reduce the effectiveness of the adhesive bond between the interface elements, so that the rotor blade sections can detach. Furthermore, moisture can enter an air pocket and attract a lightning strike to the slip connector, thereby bypassing a lightning conductor of the rotor blade.
To circumvent the inclusion of air pockets, another approach considers bonding the interface elements with a low-viscosity resin. A vacuum infusion process is set up to draw the low-viscosity resin through the interface elements. However, a vacuum infusion process is costly and complex, and must be adapted specifically to each interface shape. For rotor blades comprising three or more sections, the assembly procedure can be prohibitively expensive and time-consuming.